The quantitative determination of vitamin D by means of its growth-promoting property

Abstract

A CERTAIN amount of distrust has sometimes been felt for those methods of estimation of vitamin D in which the basal diet of the rats either had an abnormally high calcium, low phosphorus content (e.g. the McCollum diet 3143 and the Steenbock diet 2965, in both of which the ratio Ca: P is about 4:1), or was devoid of various essentials for normal nutrition (e.g. the Pappenheimer diet on which rats do not grow). Dr J. H. Burn suggested that it should be possible, with an adequate basal diet, to use the growth-promoting property of vitamin D [Steenbock, Nelson and Black, 1924] as a means of estimating that vitamin with a degree of accuracy equal to that obtained in the estima- tion of vitamin A by means of its growth-promoting property [Coward, Key, Dyer and Morgan, 1930; 1931; Coward, 1932]. We therefore decided to use the same basal diet as that used in our vitamin A determinations but, instead of giving a supplement of vitamin D throughout the preparatory and test periods and graded doses of vitamin A during the test period, we gave a supplement of carotene (for vitamin A) throughout the preparatory and test periods and graded doses of vitamin D during the test period. We found that the rats ceased to grow on the diet rich in carotene but free from vitamin D in varying lengths of time, and resumed growth on being given vitamin D. The response was graded to the dose of vitamin D given. We thus had a method of estimation of vitamin D in which the basal diet of the animals supplied all needs except that for vitamin D. It is thus free from the objections sometimes made to the diets in general use for vitamin D determinations. While these objections still seem to be theoretically sound, they do not appear to be serious from the practical considerations of vitamin D estimations, for we have obtained the same results in estimating the vitamin D content of substances by using the line test and the growth test.